Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!samsung!uunet!mcsun!cernvax!ethz!marti
From: marti@ethz.UUCP (Robert Marti)
Newsgroups: comp.lang.c++
Subject: Re: C++ Interfaces to Relational Databses.
Keywords: C++, OOP, OODBMS.
Message-ID: <2765@ethz.UUCP>
Date: 8 Dec 89 10:03:19 GMT
References: <6515@pbhyf.PacBell.COM> <1989Dec5.010812.3485@sjsumcs.sjsu.edu>
Organization: ETH Zuerich
Lines: 100

In article <6515@pbhyf.PacBell.COM> mtc@PacBell.COM (Mitchell T. Christensen)
writes:
>	[We are] unable to come up with a clean interface for C++ to our
>     "standardized" DBMS Oracle.  Is there anyone out there who has
>     solved this problem?

Yes, we believe we have solved the problem.  About two years ago, we
designed a call interface to Oracle for Modula-2 (no flames, please ;-).
Although our interface was influenced by Oracle's OCI (formerly known
as HLI), we believe that our solution should be portable to other DBMSs
which support call interfaces, e.g., Sybase.  [As an aside: Oracle's
OCI isn't all that bad once you give the procedures sensible names and
leave some of the unnecessary parameters away ...]

I have recently rewritten this interface in C++.  I feel that the concepts
of classes, overloading and default parameters all have contributed to
make the interface both safer and cleaner than the Modula-2 version from
which it was derived.  The following class SQL_Request forms the core of
our interface:

class SQL_Request {
  public:
    SQL_Request(const char* statement);
      // Create a database request which subsequently can be executed
      // several times with possibly different input parameters by
      // calling member function Execute.

    ~SQL_Request();
      // Drop the database request.

    void BindInPar(const char* colName, const char* varAdr, int size,
                   const SQL_NullInd* indAdr = 0);
    void BindInPar(const char* colName, const int* varAdr,
                   const SQL_NullInd* indAdr = 0);
    void BindInPar(const char* colName, const double* varAdr,
                   const SQL_NullInd* indAdr = 0);
      // Bind the program variable at address varAdr as an input parameter
      // to column colName in the SQL statement associated with this request.
      // (indAdr may contain the address of a null indicator variable.)

    void BindOutPar(const char* colName, const char* varAdr, int size,
                    const SQL_NullInd* indAdr = 0);
    void BindOutPar(const char* colName, const int* varAdr,
                    const SQL_NullInd* indAdr = 0);
    void BindOutPar(const char* colName, const double* varAdr,
                    const SQL_NullInd* indAdr = 0);
      // Bind the program variable at address varAdr as an output parameter
      // to column colName in the SQL statement associated with this request.
      // (indAdr may contain the address of a null indicator variable.)

    SQL_Code Execute();
      // Execute this request.
      // Note: Execute copies the values of all bound input parameters
      // from the program variables into the database columns.

    SQL_code Fetch();
      // Fetch the next row associated with this request.
      // Note: Fetch copies the values of all bound output parameters
      // from the database columns into the program variables.

  private:
    // ...
};


As an illustration, here is a simple example of how to use this
interface:

#include <stdio.h>
#include "SQL.h"

  int empNo;
  char empName[20];
  double empSal;
  SQL_NullInd nullSal;

  SQL_Request query = "SELECT empNo, eName, sal \
                       FROM Emp \
                       WHERE sal > :sal";
  query.BindInPar("sal", &empSal);
  query.BindOutPar("empNo", &empNo);
  query.BindOutPar("eName", empName, sizeof(empName));
  query.BindOutPar("sal", &empSal, &nullSal);
  printf("enter minimum salary: ");
  scanf(" %f", &empSal);
  query.Execute();
  while (query.Fetch() == SQL_ok) {
    printf("%4d     %s", empNo, empName);
    if (nullSal == SQL_null) printf("    ** null salary **\n");
    else printf("     %f\n", empSal);
  }


I hope this helps ...

-- 
Robert Marti                      Phone:      +41 1 256 52 36
Institut fur Informationssysteme
ETH-Zentrum                       CSNET/ARPA: marti%inf.ethz.ch@relay.cs.net
CH-8092 Zurich, Switzerland       UUCP:       ...uunet!mcvax!ethz!marti